I just checked the PDF manual. Taurus says to not exceed these loads.
.44 Special: 200 gr @ 900fps.
.44 magnum: 240 gr @ 1350 fps.
When I guestimate loads, I use the "powerfactor" method. This is so that I don't exceed the impulse levels that the gun is designed for. A lighter bullet can go faster than a heavier one without doing damage.
Power factor is what is used in competitive shooting to ensure that the loads are apropriate for defensive use. P.F. = M x V / 1000. So (240 x 1350) / 1000 = 324. This is just a guide line.
If you want to find the actual Muzzle Energy, it's more complicated. M.E = M x V x V /450400. Or (240 x 1350 x 1350) / 450400 = 971.xxxxxxx ft lbs.
Easy, right?
O.K. class over. There's a quiz in the morning. lol